1. Field of the Invention
This invention relates to apparatus for intraoral diagnostic studies. More particularly, the invention relates to apparatus for accurately positioning an image receptor, such as an X-ray film, in a patient's mouth in predetermined relation to an energy beam, such as an X-ray beam, to thereby enable the generation of diagnostically-useful images of portions of the patient's alveolar ridge and/or teeth. The apparatus of our invention allows precise re-positioning of the image receptor so that a series of images of predetermined target areas can be produced at successive times.
2. Description of the Prior Art
Intraoral X-ray diagnosis involves positioning an X-ray film within a patient's oral cavity next to the inner surface of the target, i.e., the teeth or alveolar bone being studied, then exposing the film to an X-ray beam generated outside the oral cavity and passing through the target. Historically, the film has been mounted in a holder which includes a bite block portion extending from the film in the direction of the external X-ray tube; the patient bites down on the bite block with the teeth comprising the target and thereby holds the film in position next to the target.
It is known that in normal dental X-ray practice, precise positioning of the X-ray film with respect to a suitably collimated X-ray beam can minimize the amount of radiation to which the patient is exposed.
A recent diagnostic technique for monitoring progressive or recurring alveolar bone loss is known as digital subtraction radiography (DSR). In this technique, the area of study is X-rayed at at least two different times. Digital computer procedures are then used to reveal any changes occurring in the target area between the initial and follow-up exposures. It is well known that reproducible positioning of the film, both with respect to the X-ray beam and especially with respect to the target area, is critical to the effective use of DSR.
In attempting to meet the need for reproducible film positioning, both for DSR and for other intraoral procedures, and to minimize the patient's exposure to radiation, prior workers have developed a number of devices which have succeeded in varying degrees. Some examples of such devices can be found in the following listed U.S. patents:
______________________________________ Film holders: 1,719,106 4,251,732 4,295,050 Film holders plus 3,745,344 connections to 4,554,676 X-ray unit: 4,598,416 4,707,847 ______________________________________
The features of the devices disclosed by the above-listed patents can be summarized as follows:
1. Virtually all of them include a bite block which extends from the film in the direction of the X-ray source--i.e., which is gripped by the patient's maxilla and mandible at or immediately adjacent to the area of study.
2. In all but one, the bite block and film holder form a unitary structure. In the one exception, U.S. Pat. No. 4,707,847, the bite block includes a sleeve which fits and is slidable along a ridge on the film holder running parallel to the film surface; however, the ridge has no locating stops for the bite block, which means that the block cannot be firmly fixed in position with respect to the film.
3. Several (e.g., U.S. Pat. No. 4,554,676) provide for slidable adjustment of the film in the vertical direction--i.e., perpendicular to the bite block, and one (U.S. Pat. No. 4,251,732) includes several different film holding slots at different points on a unitary bite block-film holder member.
4. Of the four which include structures connecting the film holder to the X-ray unit, three (U.S. Pat. Nos. 3,745,344; 4,554,676; 4,598,416) also include means to collimate the X-ray beam to limit exposure of the patient to radiation. In none of the four does the connecting structure appear to be very rigid, which means that accidental patient movements could cause deflection of the support member and thereby move the film out of precise alignment with the X-ray beam.
5. Bite registration material is commonly used on the bite block, whereby an impression of the patient's teeth made at the initial exposure provides a means of more accurately locating the film in subsequent exposures.
Although the positioning devices of the prior art have been generally successful in facilitating sequential diagnostic studies of a patient's alveolar ridge and/or teeth supported thereby, several shortcomings have existed. First, many of the prior art devices are difficult and/or complicated to set up and adjust. Second, position adjustability of the bite block with respect to the film is generally not possible, or if possible, is subject to slippage. Third, having the bite block gripped between the patient's jaws in the immediate vicinity of the target area can mean loss of film position reproducibility in the event of rapid or severe deterioration of the teeth or bone in the target area.